Legend:

Your almost complete switch to HTTPS does not eliminate the need for a rule in HTTPS Everywhere. HTTPS Everywhere still adds an additional protection against attacks such as SSLstrip. Also, as opposed to HSTS, it does not rely on a trust of first use scheme.

3

Your almost complete switch to HTTPS does not eliminate the need for a rule in HTTPS Everywhere. HTTPS Everywhere still adds an additional protection against attacks such as SSLstrip. Also, as opposed to HSTS, it does not rely on a trust on first use scheme.

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The only equivalent protection would be to HSTS preload the entire domain but that's not an option here since you said that some subdomains don't/won't support HTTPS.